1. Field of the Invention
The invention relates to a surface mount semiconductor device. More particularly, embodiments of the invention relate to surface mount semiconductor devices using a package formed by insert-molding a lead frame with a resin.
2. Description of the Related Art
Various structures for a surface mount semiconductor device are known. For example, Japanese Patent Laid-Open Publication No. 2003-007946 describes the following structure as a conventional technique. A lead frame for multiple devices is manufactured by pressing and stamping a metal board. The lead frame is then insert-molded with a resin so as to form a plurality of packages for surface mount semiconductor devices. Each package has a concave portion at its center. Then, a semiconductor chip is mounted on the lead frame that is exposed at a bottom of the concave portion of each package, and is sealed with a resin. Finally, the lead frame projecting laterally from a side face of each package is bent (e.g., using a forming process) so as to extend around the package toward a rear surface of the package via the side face.
FIG. 1 shows a part of the lead frame for multiple devices, which is used in the aforementioned surface mount semiconductor device. The shown part corresponds to one surface mount semiconductor device. The lead frame 100 includes a lead portion 101 on which a semiconductor chip is to be mounted (die-bonded) and a lead portion 102 to which one end of a bonding wire connected to the semiconductor chip at the other end thereof is connected (wire-bonded). The two lead portions 101 and 102 are separated from each other.
A package 103 is formed by insert molding with a resin on a die bonding pad 108 and a wire bonding pad 109 that are parts of the lead frame 100 at which die bonding and wire bonding are achieved, respectively. The lead portions 101 and 102 projecting laterally from a pair of opposed side faces 104 and 105 of the package 103 are bent along the side faces 104 and 105 and a rear face (not shown) of the package 103.
Elongate through holes 106 and 107 are provided at centers of the lead portions 101 and 102, respectively. Each of the elongate through holes 106 and 107 has an approximately rectangular shape that is approximately perpendicular to a projecting direction of the corresponding lead portion 101 or 102 from the side face of the package 103 when the package 103 is formed. The lead portions 101 and 102 projecting from the package 103 can be bent approximately perpendicularly along the side faces 104 and 105 of the package 103 at positions of the elongate through holes 106 and 107, respectively. The reason for providing the elongate through holes 106 and 107 is that the elongate through holes 106 and 107 can reduce cross-sectional areas of bending portions of the lead portions 101 and 102, respectively, thereby enabling the forming process to be easily performed with a smaller load, as compared with a case in which the elongate through holes 106 and 107 are not provided.
Accordingly, it is possible to suppress stress that is applied to the package 103 near positions from which the lead portions 101 and 102 project in the forming process performed for the lead portions 101 and 102, when the package 103 is formed. It is also possible to prevent occurrence of troubles such as degradation of adhesiveness between the package 103 and the lead portions 101 and 102 and breakage of the package 103, caused by a heat generated in soldering in a mounting process, heat generated from the semiconductor chip that is operating, or the like. Therefore, it is possible to prevent the electrical properties of the device from becoming poor because of poor moisture resistance caused by the above troubles.
As the length of the elongate through holes 106 and 107 becomes closer to the width of the lead portions 101 and 102, the cross-sectional areas of the bending portions of the lead portions 101 and 102 are reduced. Therefore, the lead portions 101 and 102 can be easily bent with a smaller load.
However, the above reduction of the cross-sectional area makes a thermal resistance of each lead portion 101 or 102 larger. Therefore, a property for radiating the heat generated from the semiconductor chip is degraded, thus degrading the properties of the semiconductor chip. Moreover, the lead portions 101 and 102 may be broken by vibration or impact after mounting. In this case, the semiconductor device is inoperative. In addition, the elongate through holes 106 and 107 are partially located in the package 103. Thus, when the elongate through holes 106 and 107 become larger, moisture absorption into the package 103 may proceed so as to make the properties of the semiconductor chip poor.